1. Field of the Invention
The present invention relates to a motor, and more particularly to a brushless motor.
2. Description of the Related Art
In a conventional brushless motor having a rotor made of a permanent magnet and a stator surrounding the rotor, a plurality of stator poles are formed in the yoke of the stator such that the stator poles face the periphery of the rotor. When current is supplied to stator coils wound on the yoke, repulsive forces and attractive forces are produced between the stator and the rotor due to magnetic flux induced by the current so that the rotor is rotated by the repulsive forces and attractive forces.
However, when three-phase sinusoidal current is applied to the stator coils of the conventional motor, a ripple is generated in the torque, which equals to the product of current and magnetic flux density, if the profile of magnetic flux generated at each magnetic pole of the rotor, i.e., the profile of the magnetic flux density is rectangular. The ripple is a sixth-order vibration having a frequency six times the frequency of the current.